Administering And Interpreting Visual Fields In Glaucoma


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ADMINISTERING AND INTERPRETING VISUAL FIELDS
IN GLAUCOMA
Danica J. Marrelli, OD, FAAO University of Houston College of Optometry
Visual Fields (aka Perimetry)
• The measurement of the boundaries of the field of vision and of retinal sensitivity, both centrally and peripherally. The standard of care to screen, monitor, and manage eye disease. -- Zeiss Academy
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Perimetry Basics
•Hill of Vision
•The field of vision is commonly represented as a hill or island. The height and shape of the normal hill varies by individual but is fairly consistent in normal same age individuals.
Perimetry Basics
•Visual Field Orientation
•The nasal retina sees objects in the temporal field and the superior retina sees objects in the inferior field.
Left Eye
Perimetry Basics
•The Visual Pathway
•One half of the visual field from each eye is projected to one side of the brain. Visual impulses from the right visual field of each eye will be transmitted to the left occipital lobe.
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Perimetry Basics
•Threshold
•Intensity of light that can be perceived 50% of the time and not perceived 50% of the time.

Visual Field Defects

•Defects in the visual field
• Depression: an overall reduction in the height of the hill of vision. The shape stays intact.
• Constriction: A reduction in the boundary of the field of vision.
• Blind Spot: in the temporal visual field of each eye. Located where the optic nerve is.

36dB

Dimmer Blind Spot

Actual Patient plots

Brighter

Normal Right Eye

Nasal Field

Temporal Field

Location of normal physiologic blind spot

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Normal Right Eye

Superior Field
Inferior Field

Location of normal physiologic blind spot

Visual Field Defects
•Scotomas
•Absolute defect. No retinal sensitivity – Pathology – Blockage – Blind spot
•Relative defect. Reduced retinal sensitivity – Location – Shape – Depth – Size

Visual Field Defects

•Scotomas
• Nasal Step (Glaucoma) • Arcuate or Bjerrum (Glaucoma) • Central • Centrocecal
• Involving the blind spot • Paracentral

ST SN IT IN

ST SN IT IN

ST SN IT IN

ST SN

IT

IN

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Test Strategies
• How far out do you want to test?
– CENTRAL
• 30-2 • 24-2
– FULL FIELD
• Threshold or screening?
Test Strategies
• Threshold
– Standard algorithm (“Full Threshold”) – Sita Standard
• Twice as fast as standard algorithm • Excellent reproducibility
– Sita Fast
• Faster than Sita Standard • Subject to more test-test variability • Excellent for experienced test takers
SITA Test Time Comparison
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Test Time Comparison
5.5 – 10 minutes 30-2 SS

24-2 SS

3-7 minutes

30-2 SF

24-2 SF

2-5 minutes

Administering the Test
• Correct Test • Correct Patient • Correct Trial Lens • Correct Instructions

Select Test

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Trial Lens
Trial Lens – Be Careful!
• Use Full Add in:
– Patients over 60 years old – After cataract surgery – After cycloplegia (dilation) – Patients who are more than 3.00D myopic
Patch and Position Patient
• Patch opposite eye • Adjust table to a comfortable height for patient • Align patient’s eye on video monitor so that the pupil is centered in the
target • Move the trial lens holder as close to the patient’s eye as possible
without touching the lashes
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Testing
• Place cylinder lens in slot farthest away from patient and align axis
• Place sphere lens in the slot closest to the patient (in front of the cylinder lens)
• Move lens handle to patient’s temporal side so it doesn’t bump patient’s nose
• Move the trial lens holder as close to the patient’s eye as possible without touching the lashes
Note: Use only the narrow rimmed type of trial lenses to avoid lens artifact. Wide-rimmed variety will interfere with patient’s peripheral vision and adversely effect test results.
Gaze Tracking Initialization
• Provide instructions to look at fixation target and try not to blink. Let them know the instrument is going to take a picture of their eye.
• Press Start • Gaze initialization will
begin
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Begin Test
• Now provide instructions about the test itself.
• Look only at the fixation target.
• Lights will flash one at a time in the bowl, press the button when you see a light.
• Some lights are bright and some are dim.
• You are not supposed to see all of the lights.
• Press Continue
During Testing
• Provide encouragement throughout the test.
• “You’re doing a good job”
• Give them status updates.
• “You’re about ½ way through”
• Tell patient it is OK to blink.
• “The best time to blink is when you press the button”
• Pause the test if patient needs a break.
End of Test
• Click “Save and Transmit” and “print” • Change patch to other eye, change trial
lens (if necessary) and begin again
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INTERPRETATION
RELIABILITY
• CATCH TRIALS
– FIXATION LOSSES (20%) – FALSE POSITIVES (20%)*** – FALSE NEGATIVES (33%)
• GAZE TRACKER
METHODS OF DATA PRESENTATION
• GRAYSCALE
– GIVES A GRAY TONE TO A GIVEN RANGE OF THRESHOLD VALUES (DARKER = LOWER THRESHOLD VALUE)
– QUICKLY IDENTIFIES OVERALL DEPRESSIONS
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Administering And Interpreting Visual Fields In Glaucoma